User Survey and Tests Measure Impact of OTT Bypass

Despite being a recent fraud scheme, OTT bypass is currently viewed as one of the top RAFM issues, causing millions of dollars of revenue loss to telecom operators. However, our research at EURECOM confirmed that revenue loss is not the only consequence of OTT bypass. Its effects on the network, call quality and customer experience are usually underestimated and are not well understood.

To address these issues, we conducted a comprehensive study on OTT bypass (with more than 15,000 test calls and a large-scale user survey), and demonstrated its effects on a small European operator.

Here are some of the key findings of our study:

  • OTT bypass rates can be as high as 80% from certain originations. Even worse, OTT bypass can collide with other fraud schemes (such as simbox bypass, PBX bypass, false answer supervision), further degrading the call quality and customer experience.
  • Various call anomalies are caused by OTT bypass, possibly due to implementation flaws. Moreover, OTT bypass significantly increases the Post Dial Delay (PDD), but this effect is usually concealed with a false ring tone. In practice, callers may hear the ring tone for up to a minute before the callee’s phone starts ringing.
  • None of the existing detection/prevention techniques can provide a definitive solution, in terms of accuracy, scalability, bypass direction (incoming/outgoing), and ease of deployment.
  • Our user questionnaire shows that 50% of users are aware of the OTT bypass option, even though it is buried in the application settings and never advertised. However, only 12% have disabled it.

To read more about this study, see our paper at

Merve Şahin
Merve Şahin
Merve is a researcher at the software and system security group at EURECOM in France. Her PhD studies focus on the identification and detection of fraud and abuse in telephone networks. She is also interested in the implications of telephony vulnerabilities on online security, and vice versa.